1. Field of the Invention
This invention relates to a motor control apparatus and a motor control method, more specifically, a motor control apparatus and a motor speed control method for use in aircrafts and in the space field.
2. Description of the Related Art
Conventional control of motor rotating speed using a motor-position detecting encoder is feedback control in which motor rotating speed is calculated from a change in sensor position in a control cycle of a predetermined length, and a regulated rotating speed value based on a difference between a desired value and the calculated actual value of motor rotating speed is fed to the motor.
In this control, the motor speed may decrease below normal speed, resulting in a decrease in the number of encoder output signals obtained in the control cycle. In low-speed rotation of the motor in which the interval between the encoder's output signals is longer than the control period, or length of the control cycle, the motor speed may not be detected in each control cycle, leading to decreased control accuracy.
To deal with this problem, there is known a method in which in normal-speed rotation of the motor, a first speed value detected from a change in position in one control cycle is fed back in each control cycle, while in low-speed rotation of the motor, a speed value estimated from a toque command value and a second speed value detected is fed back (see Japanese Patent Application Laid-open No. 2001-178166 Publication).
Changing the way of control depending on whether the motor is rotating at normal speed or low speed, specifically whether the change in position is greater than a predetermined value or not as in the prior art disclosed in the aforementioned publication, however, unfavorably complicates the configuration of the apparatus and the control method.
The aforementioned publication mentions that in low-speed rotation of the motor, a change in position is measured at intervals of N times the control period, but does not mention how to determine N. Thus, in the case in which the rotating speed setpoint or the actual motor rotating speed changes steeply, the technique disclosed in the aforementioned publication may not necessarily be able to maintain control stability.